Surface microstructure and high-temperature erosion resistance of FeCrAl coating after high current pulsed electron beam treatment

The work aims to increase the high-temperature resistance of FeCrAl coating against salt solution erosion by improving its surface microstructure. The FeCrAl coating with 25.5% Cr, 5.5% Al and rest Fe was prepared on 45 carbon steel by arc spraying method, and then treated once by HCPEB with the pulse width of 200 µs and energy density of 20, 25, 30 and 40 J/cm2 respectively. The morphology of FeCrAl coating before and after HCPEB treatment was studied by optical microscopy (OM) and scanning electron microscopy (SEM). The distribution of alloying elements as Fe, Cr, Al and O in the modified surface layer was measured with electron probe micro-analyzer (EPMA). The phase composition was analyzed by X-ray diffractometry (XRD). The high-temperature erosion resistance of FeCrAl coating was tested in saturated solution of Na2SO4 and K2SO4 as the erosion medium at 650°C and the erosion morphology was analyzed. After HCPEB treatment, the surface layer of FeCrAl coating was remelted and the rough and loose surface became smooth and dense. Many bulged nodules composed of Fe-Cr column grains were formed on the modified surface. The agglomeration of Al element was observed at the surface of bulged nodules and the concave parts around. With the increasing energy density of HCPEB treatment, the size of nodules became larger. Moreover, the content of Fe2O3 phase decreased in the surface layer of FeCrAl coating with the more α-Al2O3 phase formed contrarily. After the 120 hours high temperature erosion tests, the weight gain of as-sprayed FeCrAl coating was 63.8 mg/cm2 and that of HCPEB treated sample with 20 J/cm2 was 51 mg/cm2. The high temperature erosion weight gain of FeCrAl coating treated by HCPEB with pulse width of 200 µs and energy density of 20 J/cm2 is reduced by 20% compared with the original coating, while the application of HCPEB treatment with excessive high energy density deteriorates the surface microstructure and high temperature erosion resistance of FeCrAl coating. © 2020, Chongqing Wujiu Periodicals Press. All rights reserved.